as in treacherous
formal
causing harm in a way that is gradual or not easily noticed
Most people with this insidious disease have no idea that they are infected. an insidious enemy
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Example Sentences
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Recent Examples of insidious
Its aims are quieter and more insidious.
—
Alison Willmore, Vulture, 31 Jan. 2026
Real-life horror of one’s own body is the most insidious kind of body horror at play here, though James’ film offers a measure of the gorily fantastical stuff too.
—Guy Lodge, Variety, 28 Jan. 2026
This insidious development is reversing at double speed the process of self-reinforcement—the hiring of original and distinctive talent and the building of reputations for competence and probity—that brings institutions their authority.
—Sean Williams, Harpers Magazine, 27 Jan. 2026
But by the late 1950s, ICBMs emerged – and these deadly intercontinental ballistic missiles presented North America with a more insidious (and for a long time, indefensible) threat.
—Barry Scott Zellen, Hartford Courant, 22 Jan. 2026
See All Example Sentences for insidious
Alison Willmore, Vulture, 31 Jan. 2026
Real-life horror of one’s own body is the most insidious kind of body horror at play here, though James’ film offers a measure of the gorily fantastical stuff too.
—Guy Lodge, Variety, 28 Jan. 2026
This insidious development is reversing at double speed the process of self-reinforcement—the hiring of original and distinctive talent and the building of reputations for competence and probity—that brings institutions their authority.
—Sean Williams, Harpers Magazine, 27 Jan. 2026
But by the late 1950s, ICBMs emerged – and these deadly intercontinental ballistic missiles presented North America with a more insidious (and for a long time, indefensible) threat.
—Barry Scott Zellen, Hartford Courant, 22 Jan. 2026
See All Example Sentences for insidious
Recent Examples of Synonyms for insidious
Adjective
-
Conditions were treacherous and the roads were impassable.—
Jim Woods,
Chicago Tribune,
26 Feb. 2026
-
On top of treacherous road conditions, more than 100,000 Bay Staters remain in the dark and without power following Monday’s mammoth nor’easter, which, for some communities, surpassed the Blizzard of ’78 in terms of impact.—
Lance Reynolds,
Boston Herald,
25 Feb. 2026
Adjective
-
Sleek lines, warm wood tones and moody, dark finishes create a space that feels contemporary and intimate, with subtle nods to the building’s artistic past in the art hanging on the walls curated from local Denver artists.—
Sara Rosenthal,
Denver Post,
25 Feb. 2026
-
Minimal, low-profile, and finished with a subtle platform sole, these Pumas are the sneakers that go from museum-hopping to dinner reservations without missing a beat.—
Chaise Sanders,
Travel + Leisure,
25 Feb. 2026
Adjective
-
But Republicans are worried that the popular but scandal-plagued Paxton could eventually win the primary, boosting Democrats’ chances of finally flipping the seat blue after decades of false hope.—
Naomi Lim,
The Washington Examiner,
28 Feb. 2026
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That same user later posted another video acknowledging police’s statement about the false rumors, which only has about 3,000 views.—
Amanda Rosa,
Miami Herald,
27 Feb. 2026
Adjective
-
The felony charges are forgery and deceptive or fraudulent business practices.—
Michael Guise,
CBS News,
25 Feb. 2026
-
All clever touches and deceptive movement, this was the Eze Arsenal couldn’t bear to miss out on.—
Amy Lawrence,
New York Times,
23 Feb. 2026
Adjective
-
Observing human behavior confirms that for some among us, the perfidious lust for unbridled power and the imposition of cruelty in its quest know no bounds and are bereft of human decency.—
A.O. Scott,
New York Times,
3 Feb. 2026
-
However, this question has now been resurrected and amplified by conservatives as evidence of a perfidious lack of patriotism.—
Charlie Campbell,
Time,
2 Feb. 2026
Adjective
-
Unfortunately, those ideas were proven to be incorrect more than a hundred years ago.—
Big Think,
Big Think,
25 Feb. 2026
-
Republicans complained that some organizations had been listed twice in the mammoth, 693-page budget bill and others had incorrect names.—
Christopher Keating,
Hartford Courant,
25 Feb. 2026
Adjective
-
Colin Gray, at his construction job, texted him what was wrong, but the teen didn’t respond, text evidence shows.—
Eric Levenson,
CNN Money,
28 Feb. 2026
-
There are no wrong moves, only infinite possibilities.—
Talia Abbas,
Vogue,
28 Feb. 2026
Cite this Entry
“Insidious.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/insidious. Accessed 4 Mar. 2026.
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